Jet propulsion devices are known in the art of underwater vessels. For example, U.S. Pat. No. 3,079,753 describes a jet propulsion device where a wholly condensable jet of steam is produced by vaporizing seawater, fed by ram pressure into a reaction chamber. In the device of '753 patent water enters the device through water inlets in the front portion of the device's housing adjacent to the nose of the housing. The water evaporates in a reaction chamber of the '753 device, and vapor passes through exhaust nozzles and propels the device. However, when the jet propulsion device of '753 patent was launched, at higher speeds the device generated a vapor-filled Riabouchinsky cavity around its housing. Such cavities are described in literature as Riabouchinsky cavities. See, for example, Birkhoff, Jets Wakes and Cavities. Inside a Riabouchinsky cavity is a low-pressure zone, filled with water vapor. When the speed of the jet propulsion device started to grow, the radius of the Riabouchinsky cavity also started to increase. In a low pressure zone of the Riabouchinsky cavity the drag of the jet propulsion device decreased. As a result of the decreased drag and the increase of water intake due to increase of ram pressure on the water entering the device, the speed of the device kept increasing and the Riabouchinsky cavity kept growing. At a critical speed the Riabouchinsky cavity grew large enough to reduce the immersion of the tail fins of the device enough to cause the device to yaw violently and cease to operate. In other words, when the device of '753 was tested, it would uncontrollably accelerate until the low-pressure Riabouchinsky cavity around its body grew big enough, so the fins were no longer immersed in water and were unable to support a stable forward movement, causing the device to deviate erratically from the course and then stop completely. To solve these problems, a device capable of stable jet propulsion movement at high speeds is needed.